1. Field of the Invention
This invention relates to nonvolatile resistive memory elements, and more particularly, to a nonvolatile resistive memory element with a passivated switching layer and methods for forming the same.
2. Description of the Related Art
Nonvolatile memory elements are used in devices requiring persistent data storage, such as digital cameras and digital music players, as well as in computer systems. Electrically-erasable programmable read only memory (EPROM) and NAND flash are nonvolatile memory technologies currently in use. However, as device dimensions shrink, scaling issues pose challenges for traditional nonvolatile memory technology. This has led to the investigation of alternative nonvolatile memory technologies, including resistive switching nonvolatile memory.
Resistive switching nonvolatile memory is formed using memory elements that are bistable, i.e., having two stable states with different resistances. A bistable memory element can be placed in a high resistance state or a low resistance state by application of suitable voltages or currents. Voltage pulses are typically used to switch the bistable memory element from one resistance state to the other. Subsequently, nondestructive read operations can be performed on the memory element to ascertain the value of a data bit that is stored therein.
As resistive switching memory device sizes shrink, it is important to reduce the required currents and voltages that are necessary to reliably set, reset and/or determine the desired “on” and “off” states of the device, thereby minimizing power consumption of the device, resistive heating of the device, and cross-talk between adjacent devices. In addition, reliable retention of data by such devices for longer periods is highly desirable.
Because a bistable memory element formed with relatively few oxygen vacancies formed therein can result in lower operating voltages and currents, it is generally desirable to minimize the number of oxygen vacancies formed in bistable memory elements. However, a bistable memory element with a small number of oxygen vacancies is inherently more likely to experience data retention issues, since the loss or migration of even a small number of oxygen vacancies in such a memory element can change the resistive state of the memory element, thereby resulting in data loss. Thus, there is a trade-off in the design of resistive bistable memory elements between those configurations having lower operating voltages and currents, which benefit from having fewer oxygen vacancies, and those configurations having higher endurance and reliability, which benefit from having more oxygen vacancies.
In light of the above, there is a need in the art for nonvolatile resistive switching memory devices having reduced current and voltage requirements and robust data retention properties.